Anesthesia machines and ventilators provide breathing gases to a patient in a clinical setting. These breathing gases are formed by mixing gases from supplies of compressed gas such as air, oxygen, and nitrous oxide. To insure proper concentrations of the gases, flow sensors are needed in supply lines for the gases to measure the flow rates of the different, component, gases forming the breathing gases given to the patient. Many types of flow sensors are available for this application including, but not limited to, differential pressure, hot wire anemometer, turbine, and ultrasound sensors.
While these types of flow sensors can provide accurate measurement of gas flow in an anesthesia machine or ventilator, an essential problem exists in such an application of protecting the patient against a fault or failure of a flow sensor. U.S. Pat. No. 6,658,946 to Lipscomb shows a flow rate measurement system that uses a second flow rate sensor to serve as a redundant flow rate measurement device that operates on a different physiological parameter. However, the addition of another stand-alone flow sensor increases the complexity, size, and cost of the flow sensing components. Also, an additional stand-alone flow sensor may introduce an additional pressure drop in the gas supply line impeding or preventing proper operation of the apparatus.